Contact your local authority, neighbouring local authorities (council) and any local private agencies you have local to you. See which of them give you the best response and which are most helpful. If you can, speak to some local fostercarers and get the low down from them.
You'll have to be approved by just one agency, whether that's a local authority or an independent. The process can take around six months, sometimes more. I moved during the approval process but they may want you to move first - ask and see what they say.
How it works is that you will have a social worker visit you over several weeks to carry out an assessment. This will be in depth, and will cover your own experiences of being parented as well as being parents. They will want lots of references, clear police checks for every adult living in the house, they will contact ex partners too if relevant. There is also training and a preparation to foster course, some places want you to do that first, others do it during the process.
Part of the assessment will be looking at the type of child you feel you could foster - and the type of fostering you could do . Short term, long term, emergency, respite, children with disabilities, children with behavioural problems, mother and baby, young children, teens, all that sort of thing.
It is intense and can be offputting. But it is designed to keep the fostered children safe.
I hope you get a good response